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Support for IPv6 has grown by almost 20 times in the past year by one measure, but most websites still can't be reached without IPv4, the current Internet Protocol, which is near running out of unclaimed addresses.

The number of subdomains under .com, .net and .org that support Internet Protocol version 6 increased by about 1,900 percent in the year leading up to October 2011, according to an automated sampling of subdomains by Measurement Factory. The study, which was sponsored by IPv6 software specialist InfoBlox, used a script to automatically sample 1 percent of the subdomains under the three well-known top-level domains.

IPv4 only allows for about 4 billion addresses, whereas IPv6 has a nearly unlimited supply. ICANN (Internet Corporation for Assigned Names and Numbers), the global governing body for the Internet, assigned the last of the unclaimed IPv4 addresses to regional registry bodies earlier this year. Some enterprises and service providers are making a gradual transition to IPv6 using dual software stacks, but experts expect users eventually to come to the Internet without IPv4 addresses. They will need pure IPv6 communication, which most operators of websites can't offer today.

Last month, 25.4 percent of subdomains under .com, .net and .org supported IPv6, up from just 1.27 percent a year earlier. However, the long-awaited IPv6 future may not be as close as it sounds from that statistic.

All the figure means is that a DNS (Domain Name System) server can point to those subdomains using IPv6. If a user with an IPv6-only device tries to go to a website, for example, the site's registrar can match up its URL with an IPv6 address and kick back an answer to the Web surfer, said Cricket Liu, vice president of architecture at InfoBlox.

Most of the dramatic boost in the past year came when GoDaddy, one of the world's largest domain registrars, made its DNS work with IPv6. GoDaddy claims its DNS service has more than 30 million customers. Had it not been for GoDaddy, the number of subdomains supported would have grown by a bit more than double, to about 3 percent, according to Measurement Factory.

But for now, most of those DNS requests wouldn't take an IPv6-only user to an actual Web page, because less than 1 percent of all subdomains surveyed had IPv6-enabled Web servers, according to the Measurement Factory study. Likewise, there were very few IPv6 email servers. Just over 2 percent of zones were served by IPv6-compatible mail servers.

The good news is that many more operators of websites, such as GoDaddy's customers, now can serve IPv6 visitors once they have an IPv6-compliant Web server, Liu said. Along with GoDaddy, Measurement Factory cited three other major registrars, Gandi and OVH in France and Active24 in the Czech Republic, that adopted IPv6 during the period.

GoDaddy has said it plans to extend its IPv6 strategy soon by supporting the new protocol on its website hosting service. Then, companies that rely on GoDaddy instead of operating their own Web servers will be able to run an IPv6 site.

The study found France leading in IPv6 adoption, with 57 percent of subdomains in France reachable by IPv6, followed by the U.S. with 42 percent and Czech Republic with 36 percent. But its scope was limited by examining only .com, .net and .org. For one thing, that left out subdomains that are under country-level domains in Asia, where a more severe shortage of IPv4 addresses has led to strong government efforts behind IPv6 in some countries.

The sample also overlooked other top-level domains where IPv6 has been more widely adopted, such as the .gov domain of the U.S. government and the .edu domain used by universities, said Nav Chander, an Internet infrastructure analyst at IDC. However, the move to pure IPv6 networking remains slow, Chander said. "There's still very little IPv6 usage," he said.